判断scrollView的滑动方向（二）

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    CGFloat yoffset = scrollView.contentOffset.y;
    CGPoint vel = [scrollView.panGestureRecognizer translationInView:scrollView];
    if (vel.y < -40) {
        //向上拖动
    }else if (vel.y > 40) {
        //向下拖动
    }else if (vel.y == 0) {
        //停止拖拽
    }
}